This invention relates to an automotive navigation system, and in particular to an automotive navigation system wherein a departure point, a destination point, and the current point of a vehicle are displayed with respective marks on a display such as a cathode ray tube.
Such an automotive navigation system has been already proposed in Japanese Patent Application Laid-open No. 58-146814. This conventional system detects the running distance and the heading of a vehicle and computes the current position of the vehicle from those information. This system also displays a map as picture information read out from a memory on the display such as a CRT while displaying the mark indicating the current position of the vehicle which is computed on the display, whereby a driver can determine the current position of the vehicle from the map and the mark imaged on the display.
However, since an extremely numerous amount of information is required to display the picture information as a map, a storage means for storing such amount of information and therefore a navigation system per se must be correspondingly large-scaled and expensive. Accordingly, it is desirable to develop a small-sized and cheap navigation system suitable for boarding it on a vehicle.
In a case where a departure point and a destination point are predetermined, even though a map stored in the memory is displayed on the display and a mark indicating the current position of the vehicle is displayed in a superposed manner, the map to be displayed on a reduced scale is in certain conditions so small that the current position of a vehicle can not be clearly displayed. Furthermore, if the distance between the departure point and the destination point is far so as to require a plurality of sequencial maps, it is very hard and cumbersome to grasp the entire running route.
Although it is not necessarily impossible to solve these technical problems with a memory having a large capacity as well as a high speed arithmetic device, the size of the whole system becomes very large so that it is difficult to board the same on the vehicle.
On the other hand, there have been disclosed, "Cathode-Ray Tube Information Center with Automotive Navigation" published in SAE Technical Paper Series 840313 by M. W. Jarvis and R. C. Berry, and "On-Board Computer System for Navigation, Orientation, and Route Optimization" published in SAE Technical Paper Series 840485 by P. Haeussermann. Both publications are based on an international Congress & Exposition held in Detroit, Mich. on Feb. 27-Mar. 2, 1984. In the former literature, an approximate position of a vehicle is determined from the communication with a satellite, and a more accurate position is determined and displayed on the CRT by means of a self-contained navigation using an earth magnetism sensor in the vehicle. The latter literature discloses a composite system of a route guide system in trunk (main) highways using distance information and a destination indicating system within a city using distance information and heading information.